Whether they are just old enough to come, visiting, or just moving in, every new child needs to feel welcomed. Sometimes its just introducing yourself that makes the difference and asking the parents what his/her favorite thing or comfort object might be.
Here's an easy coloring page you can do on the first day or when someone is visiting. It may be just what the child (or the parents) need! Simple click it to print it.
Below are some links to Welcome Songs that you could sing. It would be fun to have a march or little dance to go with one of the songs you sing that day to welcome him or her in. Give them a sticker or something (this may be more reassuring to the adult than the child).
The most important thing is to just explain everything you are doing since often everyone is in a routine. You may want to take a minute to explain to an anxious or new parent as well. It'll help you both.